A few thoughts:
* The Rem 700 short action magazine box length is 3.080", too short for the .500 Whisper.
* You would do better to start with an action with a magnum bolt face, the 500 Whisper is based on the 460 Weatherby case, rim diameter is .590" (the 17 Rem/222 Rem/223 Rem bolt face is .378"). Of course, if you opt to replace the bolt, this is a moot point.
* Due to the extractor design on the Rem 700 action, I would suggest replacing the bolt with a bolt that takes a Sako type extractor, like the forged bolts from PTG.
* Badger Ordnance, HS Precision, and Surgeon all make a detachable magazine system for the Rem 700 actions (LA and SA).